1. Field of the Invention
The present invention relates to a remote-control light receiving unit used for electric home appliances and information communication products (personal computers etc.).
2. Description of the Related Art
In a receiving device for remote control (hereinafter referred to as remote-control light receiving unit) that receives an infrared light signal transmitted from a device for remote control that is called a “remote control transmitter” and so on, a light receiving element [e.g., photodiode chip (hereinafter referred to as PD chip)] receives the infrared light signal transmitted from the remote-control transmitter. Then, various signal processings such as amplification and waveform shaping are executed by a signal control processing device (hereinafter referred to as IC chip) so that remote control of various audio visual apparatuses such as TVs and DVDs or office automation apparatuses such as personal computers is carried out in response to the received signal.
Infrared light signals transmitted from the remote-control transmitter are digital signals. These digital signals are received at a light receiving surface of the PD chip, and the received optical signals are converted to weak electrical signals. The weak electrical signals are amplified by several tens of thousands by an amplifier circuit within the IC chip. A filter circuit [band pass filter (BPF)] extracts signals of necessary frequencies from the amplified electrical signals. Thereafter, the extracted signals are outputted by a detection circuit as digital waveform information similar to the above infrared light signals.
A remote-control light receiving unit of this type is formed by mounting and fixing the PD chip and the IC chip on a lead frame and encapsulating them in a molding resin. As the remote-control light receiving unit, there are a multi-chip type light receiving unit in which the molding resin is externally covered with a metallic case and a multi-chip type light receiving unit in which the inside of the molding resin is covered with a lead frame. In general, a distance of 10 m or more of remote control is required as a function necessary for the remote-control light receiving unit. Signal amplification processing for amplifying a weak electrical signal by several tens of thousands is, however, executed in both of the multi-chip type light receiving parts. Therefore, noise components such as electromagnetic noises that are not signals are also amplified by the amplification circuit, so that the magnitude ratio of the signal to the noise (SN ratio) cannot be secured. Consequently, it becomes impossible to extract only necessary signals. In order to prevent such a phenomenon, electromagnetic shielding is frequently performed by covering the PD chip, IC chip and peripheries thereof with a conductive resin, a metallic shielding case or the like.
It is required that a remote-control light receiving unit to be installed in an apparatus such as a TV or a DVD (digital versatile disk) apparatus (hereinafter simply referred to as “apparatus”) be positioned at the front of the apparatus in order to receive the infrared signal from a remote-control transmitter.
In a structure in which a main board is placed so as to extend in a depth direction like the TV and the like, the remote-control light receiving unit may be placed on a sub-board fitted to the main board so as to be positioned at the front of the apparatus, but it is common that the remote-control light receiving unit is placed on the main board to avoid an increase in cost (e.g., JP 2001-94124 A).
In such a case, since the apparatus takes a structure in which the remote-control light receiving unit is set far back from the front of the apparatus, there arises necessity to efficiently transfer a transmission signal from the front portion of the apparatus to a lens portion of the remote-control light receiving unit body. Thus, as taught in JP 2001-94124 A, a light guiding member (light guide) is provided from the front of the apparatus to the remote-control light receiving unit so that transmission signal light that is incident on the front of the apparatus is transferred to the remote-control light receiving unit. The light guiding member is generally an injection molded product using a thermoplastic transparent resin or an infrared light permeable resin. The light guiding member is a separate part from the remote-control light receiving unit.
Next, the structures of the remote-control light receiving unit and the light guiding member will be described with reference to FIGS. 4 to 7A, 7B. In FIG. 4, a PD chip 2 is bonded to a metallic lead frame (Iron lead frames are the mainstream. The metallic lead frame will be hereinafter simply referred to as “lead frame”) 1 with an insulative adhesive 3, while an IC chip 4 is bonded with a conductive adhesive 5. The PD chip 2 usually has a PN junction structure, and because an inverse voltage is applied to the PD chip in the case of the remote-control light receiving unit, an electric potential occurs at an N electrode on the rear surface side of the chip. Therefore, it is required that an insulating state be kept between the PD chip 2 and a PD chip mounting portion of the lead frame, which portion has a GND potential because of the structure of the lead frame 1, and an epoxy resin containing an insulating filler is used for bonding the lead frame 1 and the PD chip 2.
On the other hand, since a signal processing is executed on a surface of the IC chip 4, its rear surface is irrelevant to the signal processing. Thus, bonding to the lead frame 1 may be done with either of the conductive adhesive 5 or the insulative adhesive 3. Usually, the conductive adhesive (an adhesive prepared by mixing Ag powder with an epoxy resin and the like) 5 is used. An electrode of the PD chip 2, an electrode 6 of the IC chip 4 and an input/output lead 7 of the lead frame 1 are connected to one another with a gold wire (hereinafter referred to as Au wire) having a diameter of tens of micrometers 8. Similarly, the IC chip 4 and other input/output leads 7 are connected to one another with Au wires.
The PD chip 2 and the IC chip 4 mounted on the lead frame 1 in the above-mentioned manner are encapsulated in a thermosetting resin (hereinafter referred to as a mold encapsulation resin) 9 which is mixed with a dye that transmits infrared light and blocks visible light. Deburring and bar-resin cutting are performed on the lead frame 1 exposed from the mold encapsulation resin 9.
FIG. 6 shows a four-side view of a molded resin product having the mold encapsulation resin 9 in an injection molded state. Referring to FIG. 6, injection molding is performed so that the mold encapsulation resin 9 of the molded resin product is covered with a conductive thermoplastic resin 11 (hereinafter referred to as secondary molding). Tie-bar cutting and soldering are performed on the lead frame 1 exposed from the mold encapsulation resin 9. In this manner, the input/output leads 7 of the lead frame 1 are separated from one another to be individual input/output leads 12. Subsequently, the resultant lead frame goes through a single-piece cutting process whereby a lead frame as a single article is obtained.
A method of installing the thus formed remote-control light receiving unit in an apparatus such as a TV or the like, and a method of transferring incident light will be described below.
FIG. 7A and FIG. 7B respectively show a front elevational view of the apparatus, in which a remote-control light receiving unit is installed, and a cross sectional view taken along line 7B-7B of FIG. 7A. In FIGS. 7A and 7B, a main board 15 is placed so as to extend in a depth direction of the apparatus, and an individual remote-control light receiving unit 16 as shown in FIG. 6 is provided on the main board 15 with its input/output terminals erect. On the other hand, a light receiving window 17 for transmission signal light, which is positioned at the front of the apparatus, is provided in an outer frame (which is a plastic molded product in many cases) 18 of the apparatus. An interspace from the light receiving window 17 to the remote-control light receiving unit 16 is made up for with a light guiding member (lightguide) 19 so that the transmission signal light reaches a lens of the remote-control light receiving unit 16 from the light receiving window 17.
However, the conventional remote-control light receiving unit has the following problem. That is, since the remote-control light receiving unit 16 is an electric component, it requires to be mounted on a wiring board having a wiring pattern. On the other hand, since the remote-control light receiving unit 16 also must serve as a light receiving component, it requires to be positioned at the front of the apparatus. In order to satisfy both of these conditions, the light guiding member 19 is provided. However, the light guiding member 19 is fitted to the outer frame 18 of the apparatus, and the remote-control light receiving unit 16 is fitted to the main board 15. That is, the light guiding member 19 and the remote-control light receiving unit 16 are provided at different supports. Therefore, positioning accuracy between the light guiding member 19 and the remote-control light receiving unit 16 tends to be poor.
When displacement between the light guiding member 19 and the remote-control light receiving unit 16 is large, transmission signal light emitted from the light guiding member 19 is not efficiently transferred to the lens portion of the remote-control light receiving unit 16, so that the reach of the transmission signal light from the remote-control transmitter is reduced. Furthermore, if there is a gap between a terminal end portion of the light guiding member 19 and the lens portion of the remote-control light receiving unit 16, the angle of light emitted from the light guiding member 19 may be biased or the light may be dispersed depending on the angle of transmission signal light that is made incident on the light guiding member 19, so that the light is not efficiently emitted toward the lens portion of the remote-control light receiving unit 16. Consequently, the transmission signal light from the remote-control transmitter has a reduced reach.